Light olefins, such as ethylene, propylene and butylenes, can be produced using various processes such as steam cracking, fluid catalytic cracking, conversion of methanol to olefins, paraffin dehydrogenation, alcohol dehydration, methane coupling and Fischer Tropsch reactions. However, these processes often produce varying levels of acetylenic or diene by-products, such as acetylene, methyl acetylene (MA), propadiene (PD), butyne and butadiene. These by-products must be removed from the light olefin streams because they can act as poisons to the downstream processing catalysts, such as polymerization catalysts. The preferred method of removing these by-products is by selective hydrogenation in which, for example, the acetylenes are converted to ethylene, methyl acetylene and propadiene are converted to propylene, and the butyne and butadiene are converted to butylenes.
Currently, the commercial catalysts used for this selective hydrogenation comprise nickel or palladium, such as palladium and silver, on an alumina support. However, in addition to producing the desired olefin products, these catalysts tend to generate significant quantities of saturates (for example, ethane, propane and butanes) as a result of over-hydrogenation and green oil (olefin oligomers) as a result of competing oligomerization reactions. Both of these by-products are undesirable in that they reduce the selectivity to the required light olefins. However, the green oil is particularly problematic in that it decreases the life of the hydrogenation catalyst.
There is therefore a need for an improved catalyst for the selective hydrogenation of alkynes and diolefins, wherein the catalyst exhibits increased olefin selectivity and reduced selectivity to saturates and oligomers, such as green oil, while retaining high hydrogenation activity.
U.S patent application Publication No. 2002/0068843 discloses a catalyst for selectively hydrogenating acetylenic and diolefinic compounds with low green oil formation, the catalyst comprising the following active components loaded on a porous inorganic support: (1) at least one of platinum, palladium, nickel, ruthenium, cobalt, and rhodium; (2) at least one of silver, copper, zinc, potassium, sodium, magnesium, calcium, beryllium, tin, lead, strontium, barium, radium, iron, manganese, zirconium, molybdenum, and germanium; (3) at least one rare earth metal selected from scandium, yttrium and Lanthanides in Group IIIB of Periodic Table of Elements; and (4) bismuth. Preferably, component (1) is platinum or palladium component (2) is silver, potassium or sodium and component (3) is lanthanum or neodymium.
U.S. Pat. No. 6,255,548 discloses a method for selectively hydrogenating a feed comprising an acetylenic compound and/or a diolefin in the presence of a catalyst comprising at least one support, at least one Group VIII metal selected from nickel, palladium, platinum, rhodium, ruthenium and iridium and at least one additional element M selected from germanium, tin, lead, rhenium, gallium, indium, thallium, gold, and silver, wherein the catalyst is formed by introducing said additional element M into an aqueous solvent in the form of at least one water-soluble organometallic compound comprising at least one carbon-M bond. The preferred Group VIII metals are nickel, palladium and platinum and the preferred additional elements M are germanium, tin, gold, and silver. There is no specific disclosure of a catalyst comprising rhodium and indium and no indication is given as to the molar ratio of the Group VIII metal to the additional element M, especially if the Group VIII metal is rhodium and/or M is indium.
U.S. Pat. No. 5,877,363 discloses a process for the removal of acetylenes and 1,2-butadiene from a C4 aliphatic hydrocarbon stream by contacting the hydrocarbon stream with hydrogen in a distillation column reactor containing a bed of hydrogenation catalyst comprising a GroupVIII metal selected from platinum, palladium, rhodium or mixtures thereof; optionally in combination with a Group IB or Group VIB metal, and fractionally distilling the reaction mixture to remove a heavier fraction and removing a fraction overhead comprising substantially all of the C4 compounds having reduced acetylenes and 1,2-butadiene content. The preferred hydrogenation catalyst is palladium.
U.S. Pat. Nos. 5,356,851 and 5,364,998 disclose a catalyst and a process for the selective hydrogenation of unsaturated compounds, wherein the catalyst contains 0.1 to 10%, preferably 0.2 to 5%, of at least one Group VIII metal selected from nickel, palladium, platinum, rhodium and ruthenium and 0.01 to 10%, preferably 0.1 to 5%, of at least one Group IIIA metal selected from gallium and indium. The molar ratio of Group IIIA metal to Group VIII metal is between 0.2 and 5, preferably between 0.3 and 2. The metals are deposited on a catalyst support, such as silica, alumina or silica-alumina, by (a) impregnating the support with a solution of a Group IIIA metal compound precursor, then (b) impregnating the product of (a) with a solution of a Group VIII metal compound and then (c) calcining the product of (b) at 110 to 600° C. The preferred Group VIII metals are nickel, palladium and platinum. There is no specific disclosure of a catalyst comprising rhodium and indium.
In U.S. Pat. No. 4,691,070 a catalyst for the hydrogenation of a diolefin is disclosed in which palladium or a compound thereof and at least one co-catalyst component selected from ruthenium, rhodium, cobalt, and rhenium are supported each in the form of an elemental metal or a metal compound on a non-acidic support.
A rhodium catalyst is disclosed in U.S. Pat. No. 4,420,420 in which active rhodium metal is supported on a silica type or titania type support, optionally together with one or more co-catalysts including alkaline earth metals, such as calcium, magnesium, barium and the like, noble metals, such as platinum, palladium, iridium, ruthenium, gold and the like, iron, nickel, cobalt, cerium and manganese.